|This amp is just a more powerful brother of the above. The output
transistors are not darlingtons anymore. |
The bias current is 55 mA. The output coil is 16 turns of 1.5mm wire on an 8mm diameter.
The best visible difference is seen in the input stage - the differential amp has 5 transistors in each branch instead of three. The two additional transistors, T7+T8 / T9+T10, take over the voltage, while the rest is responsible for the amplification. The T1 to T6 don't have to carry the high voltage and can be low-noise types, while T7 to T10 carry the voltage.
The author says there's another important advantage - this solution subdues Miller's feedback CB capacities of the differential amplifiers which improves slew rate and thus distortion on high frequencies.
Also the transistors of the differential amplifier work at a constant voltage which improves linearity and th us contributes to lower distortion.
The trafo should be about 2*40 Volts and 12 to 15 Amps.